If we look at upper trap growth from a Hypertrophy standpoint, we would use heavy, high rep shrugs. Mechanical tension, metabolic stress, muscle damage… all 3 mechanisms of hypertrophy are there.

But what about Hyperplasia?

This gets hazy because there is no direct evidence in humans. In order to research it, you’d have to kill the subject and/or remove an entire muscle from the body. Then you’d have to manually count all fibers (which can be hundreds of thousands). Not practical in humans. But not an issue for birds.

Bird Gains

In Birds: According to the Avian stretch model, hang weight off a bird’s wing and leave it there. Over time, the bird gets jacked. In one study by Alway et al., 30 days of stretching in 34 birds averaged 171.8 +/- 13.5% increase in muscle mass and fiber number increased 51.8 +/- 19.4%. Chronic stretch induced Hyperplasia. Study here and here.

In humans: Autopsies on 7 right-handed men showed that the left anterior tibialis muscle was larger and had more total fibers than the right muscle. The researchers implied “long-term asymmetrical low-level daily demands on muscles of the left and the right lower leg in right-handed individuals provide enough stimuli to induce an enlargement of the muscles on the left side, and that this enlargement is due to an increase in the number of muscle fibres (fibre hyperplasia).” Study here.

What to do:

Enjoy!

Lift heavy things often. It’s not the same chronic stretch as the Avian stretch model or what’s happening at the contralateral tibialis anterior, but it’s a similar idea. Instead of a full month (or lifetime) of constant stretch, you could accumulate years of intermittent stretch from heavy deads, carrying dumbbells, and loading/unloading/carrying weight.